I have found the following regarding tooltip where several people are requesting to add the $ OR % sign.The problem with that is, as per below sample, all tooltip have the same displayed format.So if you have multiples columns in different format you are screwed.

For percentage numbers, it is not possible to use a custom format as for currency because IB apply the Custom Numeric Format Stings as defined at:Custom Numeric Format Stringsand having a % sign added (such as '#.#%') result in having your value multiplied by 100 as stated in above link.